Spark ignition systems for internal combustion engines



United States Patent Inventor David Mainprize Melton, Near North F erriby, England AppL No. 776,996 Filed Nov. 19,1968 Patented Dec. 29, 1970 Assignee Joseph Lucas (Industries) Limited Birmingham, England a British company Priority Dec. 1, 1967 Great Britain No. 54835/67 SPARK IGNITION SYSTEMS FOR INTERNAL Primary Examiner-Laurence M. Goodridge Attorney-Holman, Glascock, Downing & Seebold ABSTRACT: In a spark ignition system for an internal combustion engine a spark-producing circuit is employed which on receiving an input from an oscillator produces a spark at a ggi p gg E g plug of the engine. The oscillator is coupled to the sparkrawmg producing circuit, but only oscillates when a spark is required. U.S. Cl 123/148, The oscillator is controlled by being provided with both posi- 123/149 tive and negative feedback so that when no spark is required it Int. Cl F02p 3/02 does not oscillate, and the means driven by the engine serves Field of Search 123/148E, to increase the positive feedback when a spark is required so 148DC; 3 15/209, 209T, 214 that the oscillator operates and produces a spark.

2?! L C/\ VT1 1?? j V 1?5 a 2i 5 DIST Pi BUTOR 1/ A 2 c5, 22 e4 1 2 VM/ PATENTED UEE29 wn NTOR v -5%? ATTORNEYS SPARK IGNITION SYSTEMS FOR INTERNAL COMBUSTION ENGINES This invention relates to spark ignition systems for internal combustion engines.

A system according to the invention comprises in combination an oscillator, a spark-producing circuit which on receiving an input from the oscillator produces a spark at a plug of the engine, means coupling the oscillator to the spark-producing circuit, and means driven by the engine for controlling the oscillator to determine the instants at which sparks are produced, said oscillator being provided with both positive and negative feedback so that when no spark is required the oscillator does not oscillate, and said means driven by the engine serving to increase the positive feedback when a spark is required and so cause the oscillator to operate.

One example of the invention is illustrated in the accompanying drawings, in which;

FIG. 1 is a circuit diagram; and

FIG. 2 illustrates a transformer core utilized in FIG. 1.

Referring first to FIG. 1, there are provided positive and negative supply lines ll, 12 which are connected in use to the battery of a road vehicle. There is further provided a NPN transistor VTl the collector of which is connected to the line 11 and the emitter of which is connected to the line 12 through the primary winding L3 of a transformer a resistor R4 in series, the resistor R4 being bridged by a capacitor C2. The base of the transistor W1 is connected to the line 11 through a resistor R1, and is further connected to the emitter of the transistor VTl through parallel paths one of which contains a diode D1, and the other of which contains in series a capacitor C1, a resistor R2 and a pair of feedback windings L1, L2 forming part of the transformer, the windings L1, L2 being coupled magnetically to the winding L3.

The junction of the winding L3 and resistor R4 is connected through a capacitor C3 to the base of an NPN transistor VT2,

the base of which is also connected to the line 12 through a resistor R6 and a diode D2 in parallel. The emitter of the transistor VT2 is connected to the line 12, whilst its collector is connected to the line 11 through a resistor R7, and is further connected through a resistor R8 to the base of an NPN transistor VT3. The transistor VT3 has its emitter connected to the line 12 through a resistor R10, its collector connected to the line 11 through a resistor R9, and its collector further connected to the base of the transistor VT2 through a capacitor C4 and'resistor R5 in series.

The emitter of the transistor VT3 is also connected to the base of an NPN transistor VT4, the emitter of which is connected to the line 12, and the collector of which is connected to the line 11 through the primary winding 13 of an ignition coil 14, the secondary winding 15 of which is connected to the plugs 22 of the engine through a distributor 21 in the usual way. Finally, the collector and emitter of the transistor VT4 are bridged by a voltage dependent resistor VDRl.

The windings L1, L2, L3 are arranged on an E-shaped ferrite core shown in FIG. 2, and a part rotating with the engine carries a ferrite rod 17 which, at the instant when a spark is required, is positioned above the center limb and the limb carrying the coil L2, so that it substantially increases the coupling between the coils L2, L3. The coils L1 and L2 are connected in opposition, the coil Ll providing negative feedback to the base of the transistor VTl and being provided with more turns than the coil L2, which provides positive feedback, so that when the rod 17 is not above the core 16, the coupling between the coils L2 and L3 is insufficient to cause the oscillator incorporating by the windings L1, L2, L3 and the transistor VTI to operate. However, in this quiescent condition, current flows through resistor R1 to the base of the transistor T1 so that a small current flows in the collectoremitter path of the transistor VTI. However, when the rod 17 is above the core, the coupling between the cores L2, and L3 is considerably increased, so that the overall feedback to the base of the transistor VTl is positive and the circuit oscillates at a high frequency ofabout 500 KHz to 5 MHz. The subsequent relatively high pulses of current passing through the transistor VTI are integrated by the capacitor C2 to provide a sharply rising voltage across the resistor R4, this voltage being differentiated by the capacitor C3 to provide a pulseinto the base of the transistor VT2.

In the quiescent condition, the transistors VT3 and VT4 are conducting and current is flowing in the primary winding 13 of the ignition coil. However, when the rod 17 appears above the coil 16, the pulse transmitted through capacitor C3 turns transistor VT2 on, so removing base current from transistor VT3, which in turn removes base current from transistor VT4 so that the current flowing in the winding 13 drops, and a spark is produced in the usual way, it being appreciated that the rod 17 appears above the core 16 at the instant when a spark is required. The monostable circuit constituted by transistors VT2 and VT3 and their associated components reverts to its stable condition with transistor VT2 nonconducting after a period determined by capacitor C4 and resistor R5, and diode D2 ensures that capacitor C3 discharges in readiness to produce another spark the next time the oscillator is caused to operate. The period of the monostable circuit is chosen so that at any engine speed only one spark is produced at each plug.

By virtue of the fact that the oscillator used starts suddenly when the coupling between the coils L2 and L3 is increased, the spark is produced substantially instantaneously when the ferrite rod 17 passes over the core 16. It has previously been proposed to use an oscillator which oscillates continuously in use and is coupled to the spark producing circuit, by way of means driven by the engine, when a spark is required. Such a system works well, but is difficult to manufacture because for best results it is necessary to tune the oscillator to the spark producing circuit, which is an undesirable step in manufacturing such a system because it involves the use of electronic testing equipment. It has also been proposed previously to use an oscillator which operates only when a spark is required, the oscillator being a simple arrangement in which positive feedback is provided, under the control of means driven by the engine, when a spark is required. Such an arrangement is extremely difficult to make because unless the parameters are chosen extremely carefully and controlled accurately the oscillator cannot be made to operate at exactly the right time to produce a spark. The present invention has overcome this tolerance problem by its use of both negative and positive feedback with the positive feedback being increased at the instant when a spark is required.

The arrangement described has the advantage that the capacitors C2, C3 and everything to the left thereof can be built into the casing of the distributor 21.

lclaim:

l. A spark generating system for an internal combustion engine having spark plugs, comprising in combination an oscillator, said oscillator including an output winding, a positive feedback winding, and a negative feedback winding, said positive and negative feedback windings being magnetically coupled to said output winding, biasing means driving said oscillator to a quiescent state wherein current flows in said output winding and said negative feedback winding overcomes the effect of said positive feedback winding so that said oscillator remains in said quiescent state without oscillating, a spark producing circuit for producing sparks at said plugs in turn, said spark producing circuit operating on receipt of an input, AC coupling means interconnecting said output winding and said spark producing circuitto provide an input to said spark producing circuit when the oscillator oscillates, and magnetic means driven by the engine, said magnetic means increasing the coupling between said output winding and said positive feedback winding at the instant when a spark is required, said increased coupling causing the oscillator to operate.

2. A spark generating system as claimed in claim 1 in which the oscillator comprises a transistor having said output winding in its collector-emitter path, and said positive and negative feedback windings in its base circuit.

4. A spark generating system as claimed in claim 3 in which the period of the monostable circuit is such that only one spark is produced at each plug irrespective of engine speed.

5. A spark generating system as claimed in claim 1 in which the spark generating circuit supplies sparks to the plugs by way of a distributor within which are housed the oscillator and the means driven by the engine. 

